It is believed that contemporary fuel injectors must be designed to accommodate a particular engine. The ability to meet stringent tailpipe emission standards for mass-produced automotive vehicles is at least in part attributable to the ability to assure consistency in both shaping and aiming the injection spray or stream, e.g., toward intake valve(s) or into a combustion cylinder. Wall wetting should be avoided.
Because of the large number of different engine models that use multi-point fuel injectors, a large number of unique injectors are needed to provide the desired shaping and aiming of the injection spray or stream for each cylinder of an engine. To accommodate these demands, fuel injectors have heretofore been designed to produce straight streams, bending streams, split streams, and split/bent streams. In fuel injectors utilizing thin disc orifice members, such injection patterns can be created solely by the specific design of the thin disc orifice member. This capability offers the opportunity for meaningful manufacturing economies since other components of the fuel injector are not necessarily required to have a unique design for a particular application, i.e. many other components can be of common design.
Another concern in contemporary fuel injector design is minimizing a volume downstream of a needle/seat sealing perimeter and upstream of the orifice hole(s). As it is used in this disclosure, this volume is known as the “sac” volume. This sac volume is related to the maximum depth or height of a dimpled surface extending from the orifice disc. As a practical matter, the practical limit of dimpling a geometric shape into an orifice disc pre-conditioned with straight orifice holes is the maximum depth or height required to obtain the desired spray angle(s). As the depth of the geometry is increased in order to obtain the large bending and splitting spray angles, the amount of individual hole and dimple distortion also increases and the sac volume may increase to a volume larger than is desired. Notwithstanding the potential increase in sac volume when the orifice disc is dimpled in order to obtain large values of bending and splitting spray angles, the disc material, in extreme cases, may shear between holes or at creases in the geometrical dimple, thereby rendering the orifice disc unsuitable to function as desired, such as, for example, metering fuel flow.
It is believed that a known orifice disc can be formed in the following manner. A flat orifice disc is initially formed with an orifice that extends generally perpendicular to the flat orifice disc, i.e., a “perpendicular” orifice. In order to achieve a bending or splitting angle, i.e., an angle at which the orifice is oriented relative to a longitudinal axis of the fuel injector, the region about the orifice is dimpled—such that the flat orifice disc is no longer generally planar in its entirety but is now provided with a multi-facetted dimple. As the orifice disc is dimpled, the material of the orifice disc is forced to yield plastically to form the multi-facetted dimple. The multi-facetted dimple includes at least two sides extending at a dimpling angle, i.e., the angle at which the planar surface of the facet on which the orifice is disposed thereon is oriented relative to the originally flat surface towards an apex. Since the orifice is located on one of the sides, the orifice is also oriented at a bending angle β. Because the orifice originally extends perpendicularly through the flat surface of the disc, i.e., a “base” plane, a bending angle of the orifice, subsequent to the dimpling, generally approximates the dimpling angle. And depending on the physical properties of the material such as, for example, thickness and yield strength of the material, it is believed that there is an upper limit to the dimpling angle, as too great a dimpling angle can cause the material to shear, rendering the orifice disc structurally unsuitable for its intended purpose.